Aqueous Dispersion Of Biodegradable Polyester and Process For Preparing The Same

ABSTRACT

An aqueous dispersion of a biodegradable polyester, which comprises a copolymer of 3-hydroxybutylate and 3-hydroxyhexanoate having a weight average molecular weight of 50,000 to 3,000,000 and a flexural modulus of 100 to 1500 MPa, wherein the copolymer has an average particle diameter of 0.1 to 50 μm in the aqueous dispersion. The aqueous dispersion of a biodegradable polyester is excellent in film forming characteristics and can provide a resin coating film which is soft, exhibits good elongation and is proof to bending, when it is applied to a coating material, an adhesive agent, fiber texturing, sheet or film processing, paper conversion or the like.

FIELD OF THE INVENTION

The present invention is directed to polymer products, including, butnot limited to, films, fibers, nonwovens, and sheets, obtained bystretching a composition comprising a biodegradable polyhydroxyalkanoatecopolymer. The products exhibit a desirable combination of softness andelasticity while maintaining strength. The products are useful forvarious biodegradable articles including diaper topsheets, diaperbacksheets, garbage bags, food wrap, disposable garments and the like.

BACKGROUND OF THE INVENTION

Biodegradable polymers and products formed from biodegradable polymersare becoming increasingly important in view of the desire to reduce thevolume of solid waste materials generated by consumers each year.

In the past, the biodegradability and physical properties of a varietyof polyhydroxyalkanoates have been studied. Polyhydroxyalkanoates arepolyester compounds produced by a variety of microorganisms, such asbacteria and algae. While polyhydroxyalkanoates have been of generalinterest because of their biodegradable nature, their actual use as aplastic material has been hampered by their thermal instability. Forexample, poly-3-hydroxybutyrate (PHB) is a natural energy-storageproduct of bacterial and algae, and is present in discrete granuleswithin the cell cytoplasm. PHB is thermoplastic and has a high degree ofcrystallinity and a well-defined melt temperature of about 180° C.Unfortunately, PHB becomes unstable and degrades at elevatedtemperatures near its melt temperature. Due to this thermal instability,commercial applications of PHB have been extremely limited.

Other polyhydroxyalkanoates, such aspoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), have also beeninvestigated. Examples of PHB homopolymer and PHBV copolymers aredescribed in the Holmes et al. U.S. Pat. Nos. 4,393,167 and 4,880,59,and PHBV copolymers are commercially available from Monsanto under thetrade name BIOPOL. Unfortunately, polyhydroxyalkanoates such as PHB andPHBV are difficult to process into films for use in variousapplications. As previously discussed, the thermal instability of PHBmakes such processing nearly impossible. Furthermore, the slowcrystallization rates and flow properties of PHB and PHBV make filmprocessing difficult. PHBV copolymers are typically produced withvalerate contents ranging from about 5 to about 24 mol %. Increasingvalerate content decreases the melt temperature of the polymer. However,owing to the relatively small changes in crystallinity, PHBV films oftenremain stiff and brittle for many applications.

Improved biodegradable copolymers are disclosed by Noda, for example inU.S. Pat. Nos. 5,498,692, 5,536,564, 5,602,227 and 5,685,756. Thebiodegradable copolymers of Noda comprise at least two randomlyrepeating monomer units (RRMUs) wherein the first RRMU has the structure[—O—CH(R¹)—(CH₂)_(n)—C(O)—] wherein R¹ is H or C1 or C2 alkyl, and n is1 or 2, and the second RRMU has the structure [—O—CH(R²)—CH₂—C(O)—]wherein R² is a C4-C19 alkyl or alkenyl, and wherein at least 50% of theRRMUs have the structure of the first RRMU. These copolymers areadvantageous in that they are biodegradable and exhibit a goodcombination of physical properties which allow their processing intofilms, sheets, fibers, foams, molded articles, nonwoven fabrics and thelike to provide a variety of useful articles. However, these copolymersare not soft and elastic while maintaining strength when they are intheir original unstretched state.

Polyhydroxyalkanoate (PHA) copolymers consisting essentially of therepeat units having relatively long alkyl pendant groups of three tonine carbons, such as polyhdroxyoctanoate, are known to exhibit soft andrubber-like elasticity with some level of strength. (See for example, K.D. Gagnon, R. W. Lenz, R. J. Farris, and R. C. Fuller, Macromolecules,vol. 25, pp. 3723-3728, 1992.) The utility of soft and elastic productsmade of such PHA copolymers, however, is severely limited by thedisappointingly low melt temperature around 60° C. The dimensionalstability of the product is compromised even at a temperature of awarehouse in summer which can reach above 80° C. Thus, a biodegradablesoft and elastic product made of polymers having a higher melttemperature range is desired.

It is often desirable to stretch thermoplastic polymers in order toalter their physical properties. Unfortunately, PHB and PHBV formbrittle products that typically break even when drawn to only a verysmall extent. Various methods have been attempted to improve thestretching processes and the resulting properties of stretched or drawnPHB and PHBV products, for example as disclosed in the Holmes U.S. Pat.No. 4,537,738 and the Barham et al U.S. Pat. No. 4,427,614. Additionalmethods are disclosed in the Safta European Reference EP 736,563 A1, theInstitute of Physical and Chemical Research European Reference EP849,311 A2, the Waldock WO reference 97/22459, Kusaka et al Pure Appl.Chem., 834(2):319-335 (1998) and Yamamoto et al, Intern. PolymerProcessing XII, (1997) 1:29-37. However, such methods have not beenparticularly successful in providing means for easily forming stretchedproducts having a certain combination of desired physical properties. Inparticular, the prior art does not provide polymer products havingsoftness and elasticity, while maintaining strength.

Accordingly, it would be advantageous to obtain polymer products whichare biodegradable and which have a desirable combination of soft andelastic properties allowing use of the products in a wide range ofapplications.

SUMMARY OF THEE INVENTION

Accordingly, it is an object of the present invention to provide newproducts and methods which overcome disadvantages of the prior art. Itis a related object of the present invention to provide polymer productsformed of compositions comprising a biodegradable polymer. It is afurther object of the invention to provide polymer products whichexhibit advantageous combinations of physical properties. It is a morespecific object of the invention to provide biodegradable polymerproducts which exhibit softness and elasticity while maintainingstrength. It is another object of the invention to provide methods foreasily forming such products. It is yet a further object of theinvention to provide articles comprising such polymer products.

These and additional objects and advantages are provided by the productsand methods of the present invention. In one embodiment, the inventionis directed to polymer products which are obtained by stretching acomposition comprising a biodegradable polyhydroxyalkanoate copolymer.The biodegradable polyhydroxyalkanoate copolymer comprises at least tworandomly repeating monomer units (RRMUs). The first RRMU has thestructure (I):

wherein R¹ is H, or C1 or C2 alkyl and n is 1 or 2. The second RRMU hasthe structure (II):

wherein R² is a C₃-C₁₉ alkyl or C₃-C₁₉ alkenyl.

Optionally, the copolymer further comprises a third randomly repeatingunit having the structure (III):

wherein m is from 2 to about 9. At least about 70 mole % of thecopolymer comprises RRMUs having the structure of the first RRMU offormula (I). Suitable polymer products include, but are not limited to,films, sheets, fibers, nonwovens, and products formed by bonding aplurality of fibers, for example nonwoven sheets and the like. Thepolymer products of the invention are advantageous in that they exhibita combination of softness and elasticity while maintaining strength.

In another embodiment, the invention is directed to methods of formingimproved biodegradable polymer products. The methods comprise stretchinga composition comprising a biodegradable polyhydroxyalkanoate copolymerat a temperature above the glass transition temperature T_(g) of thecomposition and below the melting temperature T_(m) of the composition.The biodegradable polyhydroxyalkanoate copolymer comprises at least twoRRMUs, wherein the first RRMU has the structure of formula (I) and thesecond RRMU has the fromula (II) as defined above. Optionally, thecopolymer further comprises a third RRMU, wherein the third RRMU isdifferent from the first RRMU and has the structure of formula (III), asdefined above. At least about 70 mole % of the copolymer comprises RRMUshaving the structure of the first RRMU of formula (I).

Conveniently, conventional solid state stretching may be employed. Thus,the methods of the invention comprise relatively easy steps as comparedwith many of the cumbersome methods of the prior art for producingstretched polymer products, and provide stretched polymer productshaving an advantageous combination of physical properties.

These and additional objects and advantages will be more fullyunderstood in view of the following detailed description.

DETAILED DESCRIPTION

While not intending to be bound by theory, it is believed that thestretching process, to some degree, orients the copolymer chains of theproducts according to the invention. The stretched polymer products ofthe invention unexpectedly exhibit an advantageous combination ofphysical properties, and particularly exhibit softness and elasticitywhile maintaining strength. Particularly, the stretched polymer productsof the invention exhibit both a higher strength, for example as measuredby a higher tensile stress at break, and a higher softness, for exampleas measured by a lower tensile modulus, as compared with an unstretchedproduct of the same composition. This combination of properties is ahighly unexpected outcome of a stretching process. Typically, astretching process results in products that are both stronger andstiffer (less soft), not stronger and softer. For example, for fibers,M. S. M. Mark describes in Polymer Science Dictionary, Elsevier AppliedScience, New York (1989), page 295, that “drawn or spun fibres aredeliberately oriented along their length to enhance strength andstiffness in this direction due to uniaxial orientation”, and L. E.Nielson and R. F. Landel describe in Mechanical Properties of Polymersand Composites, 2^(nd) Edition, Marcel Dekker, Inc., New York (1994),page 116 that “many highly oriented fibers have Young's moduli about anorder of magnitude greater than that of the unoriented polymers”. Forfilms, Nielson and Landel (page 116) also describe that “Biaxiallyoriented films, made by stretching in two mutually perpendiculardirections, have reduced creep and stress relaxation compared tounoriented materials. Part of the effect is due to the increasedmodulus.”

The products exhibit good elasticity in that they are able to recoverquickly when a deforming force or pressure is removed. In preferredembodiments, the elasticity exhibited by the present products is springyin that the products easily respond to an applied stress and quicklyreturn to their original shape after release of the deforming stress.This springy behavior which is exhibited by preferred products accordingto the invention may be similar to the elasticity of vulcanized rubberand certain synthetic thermoplastic elastomers. However, the presentproducts also exhibit high strength and resistance to creep, whereby theproducts resist premature deformation at low stress and resist saggingwhen used. The products of the invention also exhibit good softness inthat they can be bent, twisted or folded without breaking. In preferredembodiments, the softness is accompanied by a supple quality whichallows the materials to be readily bent, twisted or folded without anysign of injury. Thus, the present products are able to exhibit highstrength at large deformations that is generally exceeded only by highlyoriented materials, while exhibiting supple and springy characteristicsat small deformations which provide enhanced pliability or drape, i.e.,the products more easily conform to and fit more snugly around objects.Additionally, the products do not exhibit tackiness which is associatedwith many conventional elastomers without the use of powders or otherantiblock agents that may affect performance or interact negatively in adesired application. Importantly, the present products arebiodegradable.

The stretched polymer products are formed from a composition comprisinga biodegradable polyhydroxyalkanoate copolymer comprising at least twoRRMUs. The first RRMU has the structure (I):

wherein R¹ is H, or C1 or C2 alkyl, and n is 1 or 2. In a preferredembodiment, R¹ is a methyl group (CH₃), whereby the first RRMU has thestructure:

wherein n is 1 or 2. In a further preferred embodiment of the firstRRMU, R¹ is methyl and n is 1, whereby the polyhydroxyalkanoatecopolymer comprises 3-hydroxybutyrate units.

The second RRMU included in the biodegradable polyhydroxyalkanoatecopolymer has the structure (II):

wherein R² is a C3-C19 alkyl or C3-C19 alkenyl. Generally, in the RRMUof formula (II), the length of R² will, to some extent, influence thereduction in overall crystallinity of the copolymer. In a preferredembodiment, R² is a C3-C15 alkyl group or alkenyl group. In a furtherpreferred embodiment, R² is a C3-C9 alkyl group, and in a furtherpreferred embodiment, R² is a C5 alkyl group. In alternately preferredembodiments, R² is a C15-C19 alkyl or alkenyl group.

Optionally, the biodegradable polyhydroxyalkanoate copolymer maycomprise a third RRMU having the structure (III):

wherein m is from 2 to about 9, wherein the third RRMU is different fromthe first RRMU. Preferably m is from about 2 to about 5, more preferablym is about 3.

In order to obtain the advantageous combination of physical propertiesexhibited by the stretched polymer products of the present inventionwhile maintaining the biodegradability of the polyhydroxyalkanoatecopolymer, at least about 70 mole % of the copolymer comprises RRMUshaving the structure of the first RRMU of formula (I). Suitably, themolar ratio of the first RRMUs to the second RRMU in the copolymer is inthe range of from about 70:30 to about 98:2. More preferably, the molarratio is in the range of from about 75:25 to about 95:5, and even morepreferred, the mole ratio is in the range of from about 80:20 to about90:10. As a result, the polyhydroxyalkanoate copolymer suitably has anumber average molecular weight of greater than about 150,000 g/mole.While not intending to be bound by theory, it is believed that thecombination of the second RRMU's side chain R² and the indicated molaramounts sufficiently decrease the crystallinity of the first RRMU toform the copolymer with desired physical properties.

In further embodiments of the polyhydroxyalkanoate copolymer employed inthe compositions, one or more additional RRMUs may be included.Suitably, the additional RRMUs may have the structure

wherein R³ is H, or a C1-C19 alkyl or alkenyl group and p is 1 or 2,with the provision that the additional RRMUs are not the same as thefirst, second or third RRMUs.

The biodegradable polyhydroxyalkanoate copolymers can be synthesized bychemical or biological based methods as disclosed, for example, by Nodain U.S. Pat. No. 5,618,855, and Noda et al. in U.S. Pat. No. 5,942,597,both of which are incorporated herein by reference.

The compositions preferably comprise greater than about 50 weightpercent of the biodegradable polyhydroxyalkanoate copolymer, and it ispreferred that the copolymer is present as a continuous phase in thecomposition. In one embodiment, the composition may comprise thepolyhydroxyalkanoate copolymer as the only polymeric component, while inyet other embodiments, one or more additional polymers or copolymers maybe included in combination with the polyhydroxyalkanoate copolymer. Forexample, the compositions may include a combination of two or more ofsuch biodegradable polyhydroxyalkanoate copolymers, a combination of thebiodegradable polyhydroxyalkanoate copolymer as defined herein, andother polyhydroxyalkanoate copolymers, and/or additional polymericcomponents, for example additional polyester components or the like. Insuch embodiments, the biodegradable polyhydroxyalkanoate copolymerpreferably comprises at least about 50 weight percent, more preferablyat least about 60 weight percent, and even more preferably at leastabout 75 weight percent, of the composition.

The compositions may further include various nonpolymeric componentsincluding, among others, nucleating agents, antiblock agents, antistaticagents, slip agents, pro-heat stabilizers, antioxidants, pro-oxidantadditives, pigments, fillers and the like. These additives may beemployed in conventional amounts although, typically, such additives arenot required in the composition in order to obtain the advantageouscombination of softness, elasticity, and strength. Additionally, one ormore plasticizers may be employed in the compositions in conventionalamounts although again, plasticizer are typically not required in orderto obtain the advantageous combination of properties discussed above.

The upper limit of the use temperature of biodegradable polymerproducts, which exhibit a desirable combination of softness andelasticity, while maintaining strength, may be substantially higher thanroom temperature, because of the relatively high melt temperature of thepolymer used to fabricate such products. Preferably the upper limit ofthe use temperature of the products can exceed above 80° C. withoutmelting or becoming excessively soft, more preferably above 100° C.,even more preferably above 120° C.

The polymer products may be in any physical form and typically willcomprise a stretched film, sheet, fiber, or nonwoven or a product from astretched film, sheet, fiber, or nonwoven. For example, a stretchednonwoven product can be produced by stretching a nonwoven structure thathas been made by conventional means including spunbonding, melt blowing,air-laying, carding, hydroentangling, or combinations of theforementioned and the like, and in which the nonwoven can be bonded byany means known in the art, including but not limited to thermal,mechanical, chemical, or adhesive bonding. Alternatively, a plurality ofstretched fibers can be bonded to form a nonwoven web which can exhibitsimilar softness, elastic and strength properties to the previousapproach. Additionally, the stretched polymer product need not belimited to single component structures, for example, monolayer film ormonofilament fibers. The stretched polymer products can also includevarious multiconstituent products, including but not limited to (1)fiber or nonwovens having side-side, sheath-core, multiple-segment,islands-in-the-sea, and matrix-fibril morphologies, (2) coextruded filmsor sheets consisting or two or more layers, (3) film/fiber, sheet/fiber,film/nonwoven, or sheet/nonwoven composites, or (4) combinations of 1-3,as long as the PHA copolymer(s) comprise at least 50 weight percent ofthe composition, more preferably at least about 60 weight percent, andeven more preferably at least about 75 weight percent. Further, oneskilled in the art will appreciate that the level of elasticity,strength, and softness exhibited by a stretched multiconstituent polymerproduct will be influenced by the particular morphology andconfiguration, such as described in part in Polymer Blends and Alloys,M. J. Folkes and P. S. Hope (Editors), Chapman & Hall, New York (1993),and in Plastics Films, 2^(nd) Edition, J. H. Briston, Longman Inc., NewYork (1983).

The stretched polymer products may be conveniently formed byconventional solid state stretching techniques wherein the compositionis stretched at a temperature above the glass transition temperatureT_(g) of the composition and below the melting temperature T_(m) of thecomposition. Preferably, the product is obtained by solid statestretching the composition at a temperature at least 20° C. above theglass transition temperature (T_(g)+20° C.) and at least 20° C. belowthe melting temperature (T_(m)−20° C.) of the composition. The glasstransition temperature of the polyhydroxyalkanoate copolymers employedin the compositions of the invention are generally below roomtemperature, i.e., less than about 25° C. Generally, the meltingtemperatures of the copolymers are greater than about 100° C.

One skilled in the art will appreciate that the level of elasticity,including the springy characteristics, strength and softness exhibitedby the stretched product will be influenced by not only the stretchingtemperature, but also by the rate and extent of stretching, whether thestretching is carried out at a constant or variable rate ofdisplacement, strain or stress, the type of stretching and, for films,sheets, or nonwovens, whether the stretching is uniaxial or biaxial and,if biaxial, whether the stretching steps are performed sequentially,simultaneously, or some combination thereof. The stretching may beconducted at a constant or variable rate of displacement, strain orstress in accordance with techniques known in the art, for example, by atenter framing process for films, sheets, and nonwovens, such asdescribed by J. H. Briston in Plastics Films, 2^(nd) Edition, LongmanInc., New York (1983), pages 83-85, or for fiber products by a spinningoperation with Godet rolls or filament winding, such as described by J.E. McIntyre and M. J. Denton in Concise Encyclopedia of Polymer Scienceand Engineering, John Wiley & Sons, New York (1990) pages 390, 391, and395. Additionally, for films, sheets, and nonwovens, the stretching maybe performed uniformly across the form, for example as achieved in atenter framing process, or incrementally across the form, for example asin a ring-rolling operation such as described in U.S. Pat. Nos.4,116,892 and 5,296,184 where alternating parallel regions that arestretched coexist with with regions that remain virtually unstretched.Additionally, for blown films and sheets, the stretching can beperformed by the double or tubular bubble process, such as described byJ. H. Briston in Plastics Films, 2^(nd) Edition, Longman Inc., New York(1983), page 85. Further, depending upon the end use, the stretching offilms, sheets, and nonwovens may be performed uniaxially or biaxially,and, if biaxially, the stretching steps may be performed sequentially,simultaneously or any combination thereof, in accordance with techniquesknown in the art. All of the above described methods of stretchingfilms, sheets, and nonwovens, including uniform as well as incrementalstretching processes, can be used and are within the scope of thepresent invention.

The extent of stretching must exceed the yield or neck point in at leastone direction of stretch while remaining below the failure point in allstretch directions. Preferably, the product is obtained by stretchingthe composition in at least one direction to an extent greater thanabout 50% strain from its initial unstretched state, and more preferablyin at least one direction greater than about 100% strain from itsinitial unstretched state. In further preferred embodiments, the productis obtained by stretching the composition in at least one direction toan extent in the range from about 200% to about 1500% strain from itsinitial unstretched state, and more preferably in at least one directionin the range from about 300% to about 1000% strain from its initialunstretched state. Additionally, one skilled in the art will furtherappreciate that the effective strain in each stretch direction willdepend on the deformation process and geometry. For example, in auniform stretching process like fiber spinning the effective strain isdetermined by the drawdown ratio, which is the ratio of the velocity ofthe fiber exiting the Godet or stretching rolls divided by the velocityof the fiber entering the Godet or stretching rolls, and as such isproportional to the overall change in sample length. By contrast, forexample, in an incremental stretching process like ring rolling theeffective strain is determined by the draw ratio within each stretch orgauge section such as disclosed in U.S. Pat. No. 4,116,892 referencedabove, and as such is proportional to localized changes in length withineach stretch region and not generally to the overall change in samplelength.

Generally, once the stretching has been completed, the stretched polymerproduct may be cooled to below its glass transition temperature or maybe subjected to a heat-setting step where the stretched form is annealedunder strain at a temperature above the glass transition temperature ofthe composition but below the melting temperature of the composition andtypically in the range of from about T_(g)+20° C. to about T_(m)−20° C.

The solid state stretching may be conducted using any suitable apparatusknown in the art, such as discussed above. The examples set forth belowdescribe the use of an Instron universal testing machine, but one ofordinary skill will appreciate other apparatus which may be employed.The Instron or other stretching apparatus which is employed ispreferably equipped with an environmental chamber to provide a thermallycontrolled stretching process. One skilled in the art will appreciatethat the stretching conditions and the annealing conditions, ifemployed, can be determined for a given composition as described hereindepending on the desired end use application.

The stretched products of the present invention are advantageous inexhibiting a good combination of softness and elasticity whilemaintaining strength. More specifically, the stretched polymer productsof the invention exhibit (1) higher strength, for example as measured bya higher tensile stress at break, (2) higher softness, for example asmeasured by a lower Young's modulus, and (3) higher elasticity, forexample as measured by a higher percent recovery after release of thedeforming stress, as compared with an unstretched product of the samecomposition. In preferred embodiments, the stretched polymer productshave a tensile strength of greater than about 15 MPa, as measured forexample according to ASTM D882-97 for films, and preferably greater thanabout 20 MPa. Additionally, in preferred embodiments, the stretchedpolymer products have a Young's modulus of less than about 400 MPa, asmeasured for example according to ASTM D882-97 for films, morepreferably less than about 300 Ma, and even more preferably less thanabout 200 MPa.

The elasticity of the stretched products, and particularly thespringiness of the products, allows the products to substantiallyrecover when the stretched products are elongated, for example duringuse. Thus, in a preferred embodiment, the stretched polymer productsexhibit elastic behavior that results in greater than about 65% recoveryof the product in less than about 15 seconds when the product iselongated up to about 50%, as measured for example according to ASTMD5459-95 for films. More preferably greater than about 75% recovery, andeven more preferably greater than about 85% recovery.

The stretched products are useful for comprising various biodegradablearticles including disposable, environmentally benign packaging,overwrap, absorbent articles including diaper/catemenial/femininehygiene topsheets, nonwoven cores, and backsheets, stretch filmsincluding food and pallet wrap, agricultural films, mulch film,balloons, skin packaging, stretch packaging, bags including food andgarbage bags, contraceptives including condoms and diaphraghms, shrinkpackaging, synthetic paper, carpeting, fishing line, hospital gowns,gloves, band-aids, wound dressings, disposable garments including shirtsand socks, disposable surgical drapes, sutures, mailing envelopes, andagricultural uses including row covers, bed covers, turf covers, andweed barriers.

The products and methods of the present invention are furtherexemplified in the following examples. In the examples and throughoutthe present specification, parts and percentages are by weight unlessotherwise specified.

EXAMPLE 1

This example demonstrates uniaxial stretching of a melt extrusion castfilm according to the invention. Specifically, a copolymer of3-hydroxybutyrate and 8.4 mole percent 3-hydroxyoctanoate (hereafter aPHBO copolymer) is melt extruded into cast films of varying thicknessesranging from about 0.003 to about 0.004 inches. Rectangular strips ofabout 1×4 inches are cut from the film with the long dimension parallelto the machine direction of fabrication. Individual strips are placed inan Instron universal testing machine (Model 1122, Canton, Mass.) suchthat the long dimension is in the pull direction, with a test gagelength of one inch. The test machine is equipped with a Sintech ReNew™1122/R upgrade package, TestWorks™ V3.02 software for test control andanalysis, and 200 lb_(f) high/low temperature pneumatic grips (modelS512.01), all from MTS Systems Corp., Research Triangle Park, N.C., asweb as an environmental chamber, Series 3710, from MTS Direct, EdenPrairie, Minn., to provide thermally controlled uniaxial stretching. Fortests in which the stretching temperature is different from ambient, thetest strips are allowed to equilibrate for about 2-3 minutes beforestarting the stretching process. Film strips of the PHBO cast film canbe extended beyond 1500% elongation before failure. In addition, thestretched strips exhibit elastic behavior, i.e., when clamped betweenthe thumb and forefinger on each hand of a technician and then pulledapart, the film is easily extended and quickly returns to its originallength after release. This behavior demonstrates that the PHBO filmcomposition is highly ductile and the stretched PHBO film composition isspringy.

EXAMPLE 2

This Example demonstrates uniaxial stretching of a PHBO copolymer meltspun fiber according to the invention. The PHBO copolymer from Example 1is melt spun into fibers having a diameter of about 4 mm. Test strandsabout 3 inches long are cut from the PHBO fiber. Following thestretching procedure described in Example 1, using a stretchingtemperature of about 60° C. and an initial strain rate of about 2in/in-min, strands of the PHBO fiber can be elongated in excess of 1000%before failure. In addition, the stretched fiber strands exhibit anelastic behavior, i.e., when clamped between the thumb and forefinger oneach hand of a technician and then pulled apart, the fiber is easilyextended and quickly returns to its original length after release. Thisbehavior demonstrates that the PHBO fiber composition is highly ductileand the stretched PHBO fiber is springy.

EXAMPLE 3

This Example demonstrates uniaxial stretching of a comparative meltextrusion cast film. A copolymer of 3-hydroxybutyrate and 12 molepercent 3-hydroxyvalerate (hereinafter PHBV copolymer) obtained fromZeneca Bioproducts Inc. (New Castle, Del.) is melt extruded into a castfilm having a thickness of about 0.003 inches. Following the samplepreparation and stretching procedure described in Example 1 for variousstretch temperatures and initial strain rates, the PHBV film strips donot stretch past 10% elongation without breaking. This behaviordemonstrates that PHBV compositions are stiff and brittle, and generallydo not form stretched polymer products.

EXAMPLE 4

This Example demonstrates uniaxial stretching of a melt extrusion castfilm according to the invention. A copolymer of 3-hydroxybutyrate and6.9 mole percent 3-hydroxyhexanoate (hereafter a PHBH copolymer) is meltextruded into a cast film having a thickness of about 0.002 inches.Following the sample preparation and stretching procedure described inExample 1, using a stretching temperature of about 60° C. and an initialstrain rate of about 4 in/in-min, film strips of the PHBH cast film canbe extended beyond 400% elongation before failure. In addition, thestretched strips exhibit an elastic behavior, i.e., when clamped betweenthe thumb and forefinger on each hand of a technician and then pulledapart, the film is easily extended to 1.5 times its original length andquickly returns to its original length after release. This behaviordemonstrates the PHBH composition is ductile and the stretched PHBH filmcomposition is springy.

EXAMPLE 5

This Example demonstrates uniaxial stretching of another melt extrusioncast film according to the invention. A copolymer of 3-hydroxybutyrateand 9.7 mole percent 3-hydroxyoctadecanoate (hereafter a PHBOdcopolymer) is melt extruded into cast films of varying thicknessesranging from about 0.002 to about 0.005 inches. Following the samplepreparation and stretching procedure described in Example 1, using astretching temperature of about 60° C. and an initial strain rate ofabout 60 in/in-min, film strips of PHBOd cast film can be extendedbeyond 1000% elongation before failure. In addition, the stretchedstrips exhibit an elastic behavior, i.e., when clamped between the thumband forefinger on each hand of a technician and then pulled apart, thefilm is easily extended to 1.5 times its original length and quicklyreturns to its original length after release. This behavior demonstratesthat the PHBOd composition is highly ductile and the stretched PHBOdfilm composition is springy.

EXAMPLE 6

This Example demonstrates biaxial stretching of a PHBO melt extrusioncast film according to the invention. A film strip of the PHBO copolymercast film from Example 1 is first stretched about 300% according to theprocedure described in Example 1 at a temperature of about 60° C. and aninitial strain rate of about 4 in/in-min. This stretched sample is thenrotated ninety degrees within the test machine such that the firststretch direction is perpendicular to the pull direction. A secondstretch of about 300% elongation is carried out a temperature of about60° C. and an initial strain rate of about 4 in/in-min. The springynature of the resulting biaxially oriented film is readily discerned bysimply stretching the film by hand, as the film quickly returns to itsoriginal length after release of the deforming strain.

EXAMPLE 7

This Example compares tensile properties of stretched and unstretchedPHBO melt extrusion cast films. Specifically, the tensile properties ofstretched and unstretched PHBO melt extruded cast film strips fromExample 1 are determined by a method outlined in ASTM D882-97 using anInstron universal testing machine such as described in Example 1. Thestretched samples are produced at a stretch temperature of about 60° C.and an initial strain rate of about 100 in/in-min. The stretched filmsare stronger, as evidenced by a higher stress at break, softer, asevidenced by a lower Young's modulus, but less extensible, as evidencedby a lower strain at break, than the unstretched counterparts.

EXAMPLE 8

This Example demonstrates the elastic recovery of a stretched PHBO meltextrusion cast film according to the invention. The elastic propertiesof a stretched PHBO cast film from Example 1 are measured by determiningthe dimensional recovery exhibited by a film when it is stretched in anInstron universal testing machine, such as described in Example 1. Thestretched films are prepared at a stretch temperature of about 60° C.and an initial strain rate of about 100 in/in-min. The stretched filmsare extended at ambient temperature to a predetermined extension at aninitial strain rate of 1.0 in/in-min, the applied stress removed, andthe decrease in strain measured after about 10-15 seconds relaxationtime. The stretched PHBO film strips show a short-term recovery ofgreater than about 85% from up to about 100% extension. This behaviordemonstrates the long-range mechanical elasticity of the productsaccording to the invention.

EXAMPLE 9

This Example demonstrates an elastic, pliable band-aid formed fromstretched PHBO cast film according to the invention. A stretched film isprepared from a PHBO cast film of Example 1, where the stretchingprocess is carried out at a temperature of about 60° C. and an initialstrain rate of about 20 in/in-min. A 0.75×3 inch film strip is cut fromthe stretched PHBO film. An absorbent pad 0.75×1.0 inch is gluedlengthwise to the center of the strip, and self-adhering Velcro piecesare attached to the ends to form a band-aid. Use of the band-aid on anindex finger shows that the film easily flexes, and follows both theback-and-forth and bending motions of the index finger without sagging.

EXAMPLE 10

This Example demonstrates the fabrication of a springy, soft nonwovensheet from stretched PHBO fiber according to the present invention. Anonwoven sheet is prepared from stretched PHBO fibers. Melt spun PHBOfibers are stretched as described in Example 2 at a temperature of about60° C. and an initial strain rate of about 3.0 in/in-min. Several of thestretched strands are cut to 3 inch lengths and placed randomly betweentwo 10 mm think, 6×6 inch sheets of polytetrafluoroethylene (Teflon®),the whole being placed between the platens of a Carver® hydrauliclaboratory press. The upper platen is preheated to about 15° C. abovethe calorimetrically determined melting point of the PHBO, and has aequally spaced spot bonding pattern of 25 1.0 mm diameter bonds persquare inch. Sufficient pressure is applied so as to cause the bondspots to soften and fuse. The pressure is released and the nonwovensheet is allowed to cool to room temperature before removing the outerpolytetrafluoroethylene sheets. The springy nature of the nonwoven sheetis readily discerned by simply stretching the sheet by hand, as thesheet quickly returns to its original dimensions after release of theapplied strain.

EXAMPLE 11

The Example demonstrates uniaxial stretching of conventional meltextrusion cast films and tensile properties thereof. Melt extruded castfilms are made from several biodegradable polymers includingpolycaprolactone (Tone® P787, Union Carbide,), Bionolle 1001 and 3001(Showa Highpolymer Co., LTD., Tokyo, JP), Eastar 14766 (Eastman ChemicalCompany, Kingsport, Tenn.), and BAK 1095 (Bayer Corporation, Pittsburgh,Pa.), as well as from several nondegradable polymers includingpolypropylene (type 7300KF, Millennium Petrochemicals, Cincinnati,Ohio), high density polyethylene (HDPE) (type LTPR059, MillenniumPetrochemicals, Cincinnati, Ohio), and a 50:50 by weight low densitypolyethylene (LDPE):linear low density polyethylene (LLDPE) blend (typeNA940000 and GA5010110, respectively, Millennium Petrochemicals,Cincinnati, Ohio). Following the sample preparation and stretchingprocedure described in Example 1, using a stretching temperature ofabout 25° C. and an initial strain rate of about 1.0 in/in-min, filmstrips of various cast films can be extended beyond 300% elongationbefore failure. This behavior is consistent with film compositions thatare ductile.

The tensile properties of the stretched melt extruded cast film stripsare determined by the method outlined in ASTM 882-97 using an Instronuniversal testing machine such as described in Example 1. Typical ofstretching processes, the various stretched films are stronger, asevidenced by higher stress at break, but stiffer, as evidenced by higherYoung's modulus, and less extensible, as evidenced by lower stress atbreak, than the unstretched counterparts.

Comparing the tensile properties of the stretched PHBO films fromExample 7 with the tensile properties of the stretched films from thisExample shows that the PHBO films are softer than the stretched filmsformed from the conventional compositions. In fact, the stretchingprocess enhances the softness of the PHBO films, as evidenced by adecrease in the Young's modulus, whereas the conventional compositionsall show an increase in stiffness as evidenced by an increase in Young'smodulus. In all cases, the stretched films show some level of recoveryfrom small extensional deformations; however, it becomes much harder toextend the stretched films formed from the conventional compositionsbeyond relatively low elongations, compared with a stretched filmaccording to the invention. For example, a 10 lb stretching force, orequivalently a 35 MPA stress for a one inch wide film strip 0.002 inchesthick, results in an immediate 50% extension for a stretched PHBO film,whereas, the stretched films formed from the conventional compositionsat best show an immediate 8% extension.

EXAMPLE 12

This example demonstrates the fabrication of a nonwoven sheet using amelt blown process. The PHBO copolymer from Example 1 is fed into anextruder which gradually melts the polymer as it feeds the melt blowingdie. The die meters the polymer into a balancing channel that isoriented linearly in the cross machine direction and that narrows to aspinneret of several holes per linear inch. At the point of exit thepolymer strands are attentuated by heated, high velocity air. The fibersthat are formed are continuous and extremely fine, and are blown onto amoving collector screen to form the nonwoven web structure. The web isthermally bonded by passing the web through a 2-roll stainless steelstack roll on which one roll there is a spot bonding pattern of about 251.0 mm diameter bonds per square inch. The stack rolls are preheated toabout 15° C. above the calorimetrically determined melting point of thePHBO composition, and sufficient pressure is applied to the web as itpasses through the stack roll so as to cause the spot bonds to softenand fuse. The lack of elasticity is readily discerned by simplystretching the nonwoven web by hand, as the web does not easily elongateand does not return to its original dimensions after release of theapplied strain.

EXAMPLE 13

This example demonstrates the fabrication of a springy nonwoven sheetfrom a melt blown nonwoven web. Rectangular strips of about 1×4 inchesare cut from the bonded PHBO web described in Example 12, with the longdimension parallel to the machine direction of fabrication. Followingthe stretching procedure described in Example 1, using a stretchingtemperature of about 60° C. and an initial strain rate of about 1in/in-min, elongated strips of the PHBO nonwoven web can be produced.The springy nature of the stretched nonwoven sheet is readily discernedby simply stretching the sheet by hand, as the sheet is easily elongatedand quickly returns to it original dimensions after release of theapplied strain. Comparing this behavior with that of Example 10 showsthat similar springy nonwoven products can be produced by eitherstretching a nonwoven sheet made by conventional means or by fabricatinga nonwoven sheet from stretched fibers.

EXAMPLE 14

This example demonstrates the fabrication of a springy film product byincrementally stretching a PHBO film in a ring rolling operationaccording to U.S. Pat. No. 4,116,892. The melt extruded PHBO cast filmfrom Example 1 is introduced in the machine direction of manufacturethrough a pair of grooved rolls that are preheated to a temperature ofabout 60° C. The grooves are perpendicular to the machine direction ofthe film, have an approximate sinusoidal shape 3 mm deep and 3 mm apart,and produce a draw ratio of about 2. When the film is stretched toconform with the shape of the grooves, 8 groove tips simultaneouslyengage the film. The film is introduced into the nip of the intermeshinggrooved rolls rotating at about 2 RPM to produce a feed velocity ofapproximately 2 feet per minute, and wound at about 4 feet per minute.The film has relatively transparent lines at 3 mm intervalscorresponding to the contact points, or stretched areas, with undrawnopaque sections in between. The springy nature of the ring-rolled PHBOfilm is readily discerned in directions parallel to the machinedirection by simply stretching the sheet by hand, as the sheet is easilyelongated and quickly returns to it original dimensions after release ofthe applied strain. By contrast, stretching the film product indirections perpendicular to the machine direction indicates no apparentspringiness or elasticity, as the sheet does not easily elongate anddoes not return to its original dimensions after release of the appliedstrain. This example illustrates that a ring rolling operation canimpart a uniaxial or directional elastic behavior to a preferred filmproduct. This approach is also applicable for preferred sheet andnonwoven products.

EXAMPLE 15

This example demonstrates the fabrication of a stretched film product byincrementally stretching a film of Bionolle 3001 (Showa Highpolymer Co.,LTD., Tokyo, JP) in a ring rolling operation. Specifically, a meltextruded cast film of Bionolle 3001 with a thickness of about 0.002inches is ring rolled according to the procedure described in Example14, using a grooved roll temperature of about 25° C. The lack ofspringiness is readily discerned by simply stretching the ring rolledfilm product by hand in directions parallel and perpendicular to themachine direction of manufacture, as the film does not easily elongateand does not return to its original dimensions after release of theapplied strain. In fact, the ring rolling operation permanently deformsthe Bionolle 3001 film in the machine direction.

EXAMPLE 16

This example demonstrates the fabrication of a contractive film productby incrementally stretching a multilayer film in a ring rollingoperation. Specifically, the PHBO copolymer from Example 1 is coextrudedwith the Bionolle 3001 resin from Example 15 into a two-layer cast filmproduct where the thickness of the PHBO layer is about 0.002 inches andthe Bionolle 3001 layer is about 0.001 inches. This PHBO/Bionolle filmis then ring rolled according to the procedure described in Example 14,using a grooved roll temperature of about 60° C. The result of the ringrolling operation is a contractive film product, in which the PHBO layeris springy as described in Example 14 and the Bionolle 3001 layer isnonspringy and permanently deformed as described in Example 15, and inwhich the Bionolle layer forms gathers or pleats as the PHBO layercontracts upon release of an applied strain. Additionally, the Bionollelayer limits the extent to which the product is rendered elasticallyextensible, at least up to the point of initial stretching.

EXAMPLE 17

This example demonstrates the fabrication of a disposable baby diaper,where the dimensions listed are intended for use with a child in the6-10 kilogram size range. These dimensions can be modifiedproportionally for different size children, or for adult incontinencebriefs, according to standard practice.

1. Backsheet: 0.020-0.038 mm film consisting of the PHBO copolymer fromExample 1; width at top and bottom 33 cm; notched inwardly on both sidesto a width-at-center of 28.5 cm; length 50.2 cm.

2. Topsheet: carded and thermally bonded staple-length polyproplyenefibers (Hercules type 151 polypropylene); width at top and bottom 33 cm;nothched inwardly on both sides to a width-at-center of 28.5 cm; length50.2 cm.

3. Absorbent core: 28.6 g of cellulose wood pulp and 4.9 g of absorbentgelling material particles (commercial polyacrylate from NipponShokubai); 8.4 mm thick, calendered; width at top and bottom 28.6 cm;notched inwardly at both sides to a width-at-center of 10.2 cm; length44.5 cm.

4. Elastic leg bands: four individual rubber strips (2 per side); width4.77 cm; length 37 cm; thickness 0.178 mm (all the foregoing dimensionsbeing in the relaxed state).

The diaper is prepared in standard fashion by positioning the corematerial covered with the topsheet on the backsheet and gluing.

The elastic bands (designated “inner” and “outer”, corresponding to thebands closest to, and farthest from, the core, respectively) arestretched to ca. 50.2 cm and positioned between the topsheet/backsheetalong each longitudinal side (2 bands per side) of the core. The innerbands along each side are positioned ca. 55 mm from the narrowest widthof the core (measured from the inner edge of the elastic bank). Thisprovides a spacing element along each side of the diaper comprising theflexible topsheet/backsheet material between the inner elastic and thecurved edge of the core. The inner bands are glued down along theirlength in the stretched state. The outer bands are positioned ca. 13 mmfrom the inner bands, and are glued down along their length in thestretched state. The topsheet/backsheet assembly is flexible, and theglued-down bands contract to elasticize the sides of the diaper.

EXAMPLE 18

The diaper of Example 17 is modified by replacing the elastic leg bandswith the springy PHBO film product described in Example 1.

EXAMPLE 19

The diaper of Example 17 is modified by replacing the elastic leg bandswith the contractive film product described in Example 16.

The specific embodiments and examples set forth above are provided forillustrative purposes only and are not intended to limit the scope ofthe following claims. Additional embodiments of the invention andadvantages provided thereby will be apparent to one of ordinary skill inthe art and are within the scope of the claims.

1. An aqueous dispersion of biodegradable polyester comprising acopolymer of 3-hydroxybutylate and 3-hydroxyhexanoate, which has aflexural modulus of 100 to 1500 MPa and a weight average molecularweight of 50,000 to 3,000,000; wherein said copolymer within saidaqueous dispersion has an average particle size of 0.1 to 50 μm.
 2. Theaqueous dispersion of biodegradable polyester of claim 1, wherein solidcontent concentration of said copolymer within said aqueous dispersionis 5 to 70% by weight.
 3. The aqueous dispersion of biodegradablepolyester of claim 1, wherein said aqueous dispersion contains anemulsifier.
 4. A process for preparing the aqueous dispersion ofbiodegradable polyester of claim 1, wherein said copolymer is producedfrom a microorganism, which comprises a step of isolating said copolymerwithin said microorganism by disrupting said microorganism containingsaid copolymer in an aqueous dispersed state.
 5. The process forpreparing the aqueous dispersion of biodegradable polyester of claim 4,which comprises a step of separating said copolymer particles, which arepartially agglomerated, from each other by applying mechanical shearingto said aqueous dispersion.
 6. The aqueous dispersion of biodegradablepolyester of claim 2, wherein said aqueous dispersion contains anemulsifier.
 7. A process for preparing the aqueous dispersion ofbiodegradable polyester of claim 2, wherein said copolymer is producedfrom a microorganism, which comprises a step of isolating said copolymerwithin said microorganism by disrupting said microorganism containingsaid copolymer in an aqueous dispersed state.
 8. A process for preparingthe aqueous dispersion of biodegradable polyester of claim 3, whereinsaid copolymer is produced from a microorganism, which comprises a stepof isolating said copolymer within said microorganism by disrupting saidmicroorganism containing said copolymer in an aqueous dispersed state 9.A process for preparing the aqueous dispersion of biodegradablepolyester of claim 6, wherein said copolymer is produced from amicroorganism, which comprises a step of isolating said copolymer withinsaid microorganism by disrupting said microorganism containing saidcopolymer in an aqueous dispersed state.
 10. The process for preparingthe aqueous dispersion of biodegradable polyester of claim 7, whichcomprises a step of separating said copolymer particles, which arepartially agglomerated, from each other by applying mechanical shearingto said aqueous dispersion.
 11. The process for preparing the aqueousdispersion of biodegradable polyester of claim 8, which comprises a stepof separating said copolymer particles, which are partiallyagglomerated, from each other by applying mechanical shearing to saidaqueous dispersion.
 12. The process for preparing the aqueous dispersionof biodegradable polyester of claim 9, which comprises a step ofseparating said copolymer particles, which are partially agglomerated,from each other by applying mechanical shearing to said aqueousdispersion.